Organic Fatigue Possible Causes of Fatigue The causes of fatigue are not well understood. An explanation of fatigue and recovery in terms of the creation and payment of an oxygen debt is inadequate. The recovery time is too short to be explained on the basis of circulatory removal of metabolites. It is probable that fatigue and recovery are intimately associated with changes in the functional properties of nerve cells and of synaptic and neuromuscular junctions as well as with changes in the muscles themselves. Site of Fatigue Fatigue of the neuromuscular junction is easily demonstrable in the nerve-muscle preparation of the frog. If the muscle is stimulated repeatedly by way of its motor nerve, the contractions become progressively weaker and finally cease. If now the stimulating electrodes are placed directly on the muscle, nearly normal contractions may be elicited. Since the nerve fiber is considered to be practically non-fatiguable, the logical conclusion is that the neuromuscular junction is the site of fatigue when a muscle is stimulated by way of its motor nerve. In a sense, the neuromuscular junction serves as a fuse which protects the muscle from injury due to overstimulation. The general fatigue which reduces the range and power of voluntary muscular activity is largely an affair of the central nervous system. The validity of this important concept is demonstrated by the following simple experiment. If a muscle is caused to contract voluntarily fatigue halts the activity, electrical stimulation of the motor nerve (by placing the electrodes on the skin over the nerve) elicits practically normal contractions. This indicates that the fatigue in voluntary activity is somewhere in the brain or spinal cord from which arise the motor nerve impulses.. It is believed that the transmission of nerve impulses across synaptic and neuromuscular junctions is mediated by the release of a chemical transmitter, probably acetylcholine. Accordingly, it has been suggested that failure of the transmission of impulses across these junctions is due to the liberation of inadequate amounts of acetylcholine. This decrease in the production and liberation of acetylcholine at synapses has been reported to accompany fatigue and to disappear with recovery.		Home Pace Motivation Measures of Endurance Computation of Dietary Requirement Work Efficiency Maximum Steady State Work Inefficiency of Anaerobic Work Estimation of Work Efficiency Efficiency of Grade Climbing Low Economy of Slow Work Maximum Rate of Work Levers of the Body Fatigue and Recovery General Fatigue Symptoms Anxiety State Organic Fatigue Cortical Motor and Sensory Centers Effect of Exercise on Mental Work Visual Fatigue Muscular Fatigue Fatigue Prevention and Recuperation